FIG. 1 shows a trailing edge 1 of a conventional aircraft wing comprising a C-section rear spar 3 consisting of a spar web 4 and upper and lower flanges 5, 6. Upper and lower covers 7, 8 are attached to the upper and lower flanges 5, 6 of the spar 3 and extend to its rear. An upper panel 9 is attached to the upper cover 7 with a butt-strap 17. A hinge rib 2 comprises two integrally formed arms 11, 12 forming a so-called “A-frame”. The upper arm 11 is attached to the upper cover 7 via the butt-strap 17 and its foot is attached to the spar web 4. The foot of the lower arm 12 is attached to the lower cover 8 and to the spar web 4. A spoiler 13 is pivotally connected to the hinge rib 2 about a hinge line 14. An actuator (not shown) deploys the spoiler up from the neutral position shown in FIG. 1. Flexible lines 15 (such as hydraulic pipes and electrical cables) are installed in a gap 16 between the spar web 4 and the two arms 11, 12 of the hinge rib 2.
These lines 15 can be awkward to install, as they need to be pulled through the gap 16 progressively, incurring a risk of snagging or damage. Moreover, there is currently a trend on modern large passenger aircraft to minimise the size of the wing section in order to improve its aerodynamic efficiency. This continuing reduction in size, coupled with an increase in systems complexity, makes existing hinge rib designs increasingly difficult to implement.
A further problem with the conventional hinge rib design is as follows. The overhanging portions of the upper and lower covers 7, 8 converge slightly towards each other. As a result it is not possible install or remove the hinge rib 2 by moving it fore or aft respectively. This can create complications during maintenance or installation of the hinge ribs 2. FIG. 2 shows a line of hinge ribs, each attached to the web 4 of a C-section rear spar. Note that the upper and lower covers and the spoiler are omitted in FIG. 2. It should also be noted that the hinge ribs shown in FIG. 2 differ slightly from the one shown in FIG. 1. In the case of FIG. 2, the hinge ribs further comprise a base 18 which extends between the feet of the upper and lower hinge rib arms 11, 12 and is attached to the spar web 4.
The height 17 of the spar web 4 gradually decreases in an outboard direction along the span of the wing. Therefore a conventional solution to the problem identified above is to move the hinge rib inboard to a point where the height of the web 4 is such that the closed angle between the upper and lower covers no longer traps the hinge rib. Thus for example if hinge rib A is damaged and has to be removed for maintenance, it may be necessary to move it inboard to a point E before removing the hinge rib in an aft direction. This requires the otherwise unnecessary removal of neighbouring hinge ribs B, C and D, adding complexity and cost to the maintenance operation.
Using the traditional single piece A-frame design for the hinge rib also does not make optimum use of the material or billet from which the hinge rib is machined, resulting in a large amount of waste. Also the grain flow in the billet can never be fully structurally optimized as the longitudinal grain flow of the material can never be aligned to both the legs of the A-frame, which may be at angles of up to 90 degrees to each other.
Alternative hinge rib designs such as shear webs can offer a more weight optimized structural solution but may be less efficient in material cost and are worse for systems installation. Also shear webs can cause significant thermal problems as they will tend to act as baffles to any global airflow that would normally aid the cooling process along the trailing edge of the wing.